1. Field of the Invention
The present invention relates to semiconductor units, semiconductor apparatuses, methods of making the same, electrooptic apparatuses and electronic apparatuses. In particular, the invention relates to a semiconductor unit and a semiconductor apparatus prepared by transferring a semiconductor element on a work piece (e.g., substrate) composed of a material different from that of the semiconductor element, and to a method of making the semiconductor unit and the semiconductor apparatus.
2. Description of Related Art
The related art includes a technology of forming a semiconductor element on a substrate composed of a material different from that of the semiconductor element. Examples thereof include a technology of forming a GaAs surface emitting laser (vertical cavity surface emitting laser (VCSEL)), a photodetector (PD) such as a photodiode, or a high electron mobility transistor (HEMT) on a silicon semiconductor substrate, and a technology of affixing micro silicon transistors, instead of thin film transistors (TFTs) for pixels of liquid crystal display (LCD), on a glass substrate.
One example of an integrated circuit constituted from semiconductors of different materials is an opto-electronic integrated circuit (OEIC). An opto-electronic integrated circuit is an integrated circuit with an optical input/output device. Signal processing inside the integrated circuit is performed by electrical signals but input/output operation between the integrated circuit and an external component is performed by optical signals.
As the inner structures of the integrated circuit are miniaturized, the operating speed of the central processing unit (CPU) of a computer, i.e., the operating clock, is also increased. However, the signal transfer rate at the bus has almost reached its limit, and this has become the bottleneck of increasing the processing rate of computers. If signal processing can be done through optical signals at the bus, it becomes possible to significantly increase the processing rate of computers beyond this limit. In order to do so, micro light-emitting and photo-detecting elements must be mounted to the silicon integrated circuit.
Silicon, which is an indirect semiconductor, cannot emit light. Silicon must be combined with other semiconductor light-emitting elements to form an integrated circuit.
In the related art, a prospective candidate for semiconductor light-emitting elements is a surface emitting laser (VCSEL) composed of a compound semiconductor such as gallium arsenide (GaAs). However, the lattice mismatch between silicon and the surface emitting laser has prevented direct formation of the surface emitting laser on the silicon integrated circuit through a semiconductor process such as an epitaxial process.
Generally, the surface emitting laser is formed on a gallium arsenide substrate. One prospective related art method is to form surface emitting laser chips from the surface emitting lasers disposed on the GaAs substrate and mechanically mounting these chips on silicon integrated circuit substrates to integrate electrical signal transfer circuits and optical signal transfer circuits.
On the other hand, in order to enhance the areal efficiency of the semiconductor substrate on which integrated circuits are formed and in order to simplify handling after integration, the size of the surface emitting laser chip on the integrated circuit is preferably as small as possible. Ideally, the chip is of approximately the same size as when an integrated circuit is monolithically fabricated, i.e., several micrometers in thickness and several ten square micrometers in area.